sophiecarenco

Modern synchrotrons, such as SOLEIL (near Paris), propose under the same roof several beamlines that operates with all types of lights, from hard to soft X-ray, from infra-red to UV. These are as many different ways to scrutinize the nano-matter and get a fuller picture of the mechanism of formation or evolution that are at play in any environment (wet, hot, liquid, with reactive gas...).

We designed a low-temperature synthetic route for CeO₂ nanorods. We employed near-ambient-pressure X-ray photoelectron spectroscopy to monitor the cerium surface oxidation state during the initial annealing of the nanopowder, followed by exposure to a moderate pressure of H₂. We demonstrate that H₂ homolytic splitting at cerium sites is the main activation process at 100 °C, leading to the oxidation of 30% of the surface cerium atoms, while the H₂ splitting at oxygen sites was absent.

R. F. André, J.-J. Gallet, F. Bournel, S. Carenco, ChemCatChem 2024, DOI 10.1002/cctc.202400163.

While the literature contains tens of protocols to prepare cerium oxide nanoparticles from Ce(III) precursors, there is still an open question regarding the time at which the cerium oxidation occurs and the role of hydroxide phases in this process. This article identifies an oxyhydroxide phase of Ce(IV) of the chemical formula CeO(OH)₂ as a key intermediate and proposes a crystal structure for it.

R. F. André, G. Rousse, C. Sassoye, M. Avdeev, B. Lassalle-Kaiser, B. Baptiste and S. Carenco, Chem. Mater. 2023, DOI 10.1021/acs.chemmater.3c00486.

Due to the variety of cobalt crystallographic phases, forming fcc nanoparticles rather than phase mixture is a challenging endeavor. We found optimized conditions to form size-controlled fcc NiCo nanoparticles from preformed Ni nanoparticles. We then investigated the early stages of Co nucleation on the nickel using a lower stoichiometry of Co, down to 0.05 equiv. vs. Ni. We showed that cobalt reacts first on the nickel nanoparticles but easily forms cobalt-rich larger aggregates in the further steps of the reaction.

A. Palazzolo, C. Poucin, A. P. Freitas, A. Ropp, C. Bouillet, O. Ersen, S. Carenco, Nanoscale 2022, doi 10.1039/D2NR00917J.

X-ray absorption near-edge structure (XANES) is a particularly well-adapted technique to study the L_2,3-edges of Mo (2520–2625 eV). It provides information on both the electronic and local structures of metal-containing species and allows drawing structure–activity relationships. However, L_2,3-edges are difficult to interpret, especially for 4d and 5d transition metals. In this work, we provide a method for their interpretation based on a library of spectra of simple Mo compounds. We suggest using the L₃-edge to determine the oxidation state and the L₂-edge to gain insight on the geometry around Mo atoms. This method is then applied to a series of molybdenum sulfide compounds to rationalize their structures.

A.P. Freitas, R. F. André, C. Poucin, T. K.-C. Le, J. Imbao, B. Lassalle-Kaiser, S. Carenco. Guidelines for the Molybdenum Oxidation State and Geometry from X-Ray Absorption Spectroscopy at the Mo L_2,3-Edges. J. Phys. Chem. C 2021, 10.1021/acs.jpcc.1c01875.

Understanding the surface reactivity of titanium oxides Magnéli phases that contain both Ti(IV) and Ti(III) is of prime importance. This article describes a new synthetic route to 50 nm carbon-free Ti₄O₇ and Ti₆O₁₁ nanoparticles.The surface reactivity of the Magnéli nanoparticles was quantitatively evaluated under different atmospheres with synchrotron radiation-based X-ray photoelectron spectroscopy, highlighting oxidized surfaces with lower conductivity than the core. This finding sheds a new light on the charge transfer occuring in these materials.

E. Baktash, J. Capitolis, L. Tinat, C. Larquet, T. H. C. Chan Chang, J.-J. Gallet, F. Bournel, C. Sanchez, S. Carenco, D. Portehault. Chem. Eur. J. 2019, 25, 11114-20.

Bimetallic nanoparticles are widely studied, for example in catalysis. However, possible restructuring in the environment of use, such as segregation or alloying, may occur. Taken individually, state‐of‐the‐art analytical tools fail to give an overall picture of these transformations.

In collaboration with Cecile S. Bonifacio and Judith C. Yang from Pittsburg University, we studied nickel-cobalt nanoparticles exposed to reactive gases. Combination of an ensemble technique (NAP-XPS) and a local one (environmental TEM) was pivotal for describing the nanoparticles transformations.

S. Carenco, C. S. Bonifacio, J. C. Yang, Chem. - A Eur. J. 2018, 24, 12037-43.

This article describes the synthesis of bimetallic oxysulftide nanoplatelets. They could be obtained over the whole (Gd,Ce) composition range with good control of size and cristallinity.

We observed that cerium-rich nanoparticles are less stable in air than Gd-rich nanoparticles. With in situ X-ray absorption and X-ray photoelectron spectroscopy, we could demonstrate that (i) all these nanoparticles actually exhibit surface sulfate, (ii) sulfate form as a consequence of exposure to water and/or oxygen, (iii) there is a threshold of 50% Ce above which the structure is not stable anymore in air, due to the formation of Ce(IV) species.

C. Larquet, A.-M. Nguyen, M. Ávila-Gutiérrez, L. Tinat, B. Lassalle-Kaiser, J.-J. Gallet, F. Bournel, A. Gauzzi, C. Sanchez, S. Carenco, Inorg. Chem. 2017, 22, 14227-14236

Using in situ ambient-pressure X-ray photoelectron spectroscopy, the formation of nickel phosphide on the surface of a nickel foil was investigated, at temperatures like those employed to form nickel phosphide nanoparticles in colloidal route using tri-n-octylphosphine as a phsophorus source.

Our results demonstrate that even below 150 °C, significant phosphorus and carbon incorporation can occur during metal nanoparticles syntheses that employ TOP as stabilizing agent. These findings provide new insight on the surface chemistry of metal phosphide nanoparticles, increasingly employed in several fields of catalysis.

S. Carenco, Z. Liu, M. Salmeron, ChemCatChem 2017, 9, 2318–2323

Our study about cobalt boride nanoparticles, led by David Portehault, uses Near-Ambient-Pressure XPS to monitor the behavior of this CO₂ methanation catalyst.

We uncovered that the crystalline structure is not stable in reducing conditions and evolves to metallic cobalt and boron oxide. This surprising result was confirmed by NEXAFS measurements and additional characterizations.

G. Gouget, D. P. Debecker, A. Kim, G. Olivieri, J.-J. Gallet, F. Bournel, C. Thomas, O. Ersen, S. Moldovan, C. Sanchez, S. Carenco, D. Portehault. Inorg. Chem. 2017, 56, 9225–9234

Surface and core of inorganic nanoparticles may undergo profound transformations in their environment of use. Accurate description is key to understand and control surface reactivity.

Through a selection of case studies, this feature article proposes a journey from surface science to nanoparticle design, while illustrating state-of-the-art spectroscopies that help provide a relevant description of inorganic nanoparticles in the context of surface reactivity.

S. Carenco, Chem. Commun. 2018, 54, 6719-6727